Qifan Chen has uploaded a new patch set (#40). (
http://gerrit.cloudera.org:8080/16474 )
Change subject: IMPALA-10178 Run-time profile shall report skews
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IMPALA-10178 Run-time profile shall report skews
This fix addresses the current limitation in runtime profile that
skews existing in certain operators such as the rows read counter
(RowsRead) in the scan operators are not reported. A skew condition
exists when the number of rows processed at each operator instance
is not about the same and can be detected through coefficient of variation
(CoV). A high CoV (say > 1.0) usually implies the existence of
skew.
With the fix, such skew is detected for the following counters
1. RowsRead in HDFS_SCAN_NODE and KUDU_SCAN_NODE
2. ProbeRows and BuildRows in HASH_JOIN_NODE
3. RowsReturned in GroupingAggregator, EXCHANGE and SORT_NODE
and reported as follows:
1. In execution profile, a new skew summary that lists the names
of the operators with skews;
2. In the averaged profile for the corresponding operator, the list
of values of the counter across all fragment instances in the
backend processes;
3. Skew detection formula: CoV > limit and mean > 5,000
4. A new query option 'report_skew_limit'
< 0: disable skew reporting
>= 0: enable skew reporting and supply the CoV limit
Examples of skews reported for a hash join and an hdfs scan.
In execution profile:
... ...
skew(s) found at: HASH_JOIN_NODE (id=4), HDFS_SCAN_NODE (id=0)
Per Node Peak Memory Usage: ...
... ...
In averaged profiles:
HDFS_SCAN_NODE (id=2): ...
Skew details: RowsRead ([2004992,1724693,2001351],
stddev/mean=0.07, mean=1910345)
Testing:
1. Added test_skew_reporting_in_runtime_profile in
test_observability.py to verify that the skews are reported.
2. Ran Core tests successfully.
Change-Id: I91041f2856eef8293ea78f1721f97469062589a1
---
M be/src/runtime/coordinator.cc
M be/src/service/query-options.cc
M be/src/service/query-options.h
M be/src/util/runtime-profile-counters.h
M be/src/util/runtime-profile.cc
M be/src/util/runtime-profile.h
M be/src/util/stat-util.h
M common/thrift/ImpalaInternalService.thrift
M common/thrift/ImpalaService.thrift
M tests/query_test/test_hash_join_timer.py
M tests/query_test/test_observability.py
11 files changed, 241 insertions(+), 17 deletions(-)
git pull ssh://gerrit.cloudera.org:29418/Impala-ASF refs/changes/74/16474/40
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Gerrit-Project: Impala-ASF
Gerrit-Branch: master
Gerrit-MessageType: newpatchset
Gerrit-Change-Id: I91041f2856eef8293ea78f1721f97469062589a1
Gerrit-Change-Number: 16474
Gerrit-PatchSet: 40
Gerrit-Owner: Qifan Chen <qc...@cloudera.com>
Gerrit-Reviewer: Impala Public Jenkins <impala-public-jenk...@cloudera.com>
Gerrit-Reviewer: Qifan Chen <qc...@cloudera.com>
Gerrit-Reviewer: Sahil Takiar <stak...@cloudera.com>
Gerrit-Reviewer: Tim Armstrong <tarmstr...@cloudera.com>
